Word origin · etymology
Eponym.
Named after Pope Gregory XIII, who promulgated the calendar reform in 1582. Gregorian is the adjectival form of his name.
How we know · epistemology
Civil calendar convention
Gregorian arithmetic follows a defined leap-year rule. Historical documents did not adopt it everywhere at once, so a correctly calculated proleptic date may differ from the date originally recorded.
Connected concepts
Mentioned in 5 other entries
These links connect subjects and terminology. They do not establish a shared historical origin.
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.